Abstract: A theoretical analysis is made on directional drilling by catenary technique. The hole deviation at the final depth is greater by several degrees in catenary directional drilling than in the usual way on account of its angle building continuously. The deeper the well, the greater is the deviation. This paper proposes an assumption thar the interaction of the bit and rock can be considered as an elastic embedded end with non-constrained rotation. Moreover, the hole trajectory is simplified as a planar curve in our analysis. A three dimensional. model of buckling of the lower string is proposed for numerical calculation. The necessary conditions to keep the drill bit along the predicted catenary trajectory should be V'(0)=0.and u'(0)=-tgθ. An analytical solution is obtained through Laplace transform. The analysis provides useful information for selecting parameters in catenary directional drilling.

摘要： 悬链线法是一种具有独特优点的定向钻井方法。本文在文献[1]的基础上,试图通过有关理论分析,对悬链线法钻定向井的一些问题提供参考。考虑到悬链线法钻定向井需要连续造斜,且井越深其井斜角愈大;同时还注意到岩石与钻头、钻头与钻柱的互相作用,本文提出了将钻头与岩石间的相互作用抽象为弹性抗转支承,即不约束转角的弹性嵌固端的设想(图4)。此外,在分析时假定井眼轨迹为一平面曲线,建立悬链线法钻定向井下部钻柱的三维挠曲变形的计算模型;提出了保证钻头沿预定井眼轴线(悬链线)的钻进条件:V'(o)=0,U'(o)=-tgθ。通过Laplace变换获得了该问题的解析解。文末以算例说明有关计算过程,并对所给结果进行了分析讨论。

关键词: 定向井, 悬链线法, 钻柱, 钻头, 井斜角, 井眼轨迹, 水平位移, 目标点, 井眼轴线, 钻井参数